Method of and means for indicating direction



May 23, 1939.

Original Filed April 11, 1931 L. c. F. HORLE METHOD OF AND MEANS FOR INDICATIING DIRECTION 2 Sheets-Sheet 1 Receiver CURRENT IN uvmrm CWL.

INVENTOR. Lawrence C/F/Vor/e ATTORNEY.

May 23, 1939. c. F. HORLE METHOD OF AND MEANS FOR INDICATING DIRECTIQN Original Filed April 11. 1931 2 Sheets-Sheet 2 f wm m m m my Wm Patented May 23, 1939 UNITED STATES gram OFFEQE Lawrence C. F. Horle, Newark, N. J.

Continuation of application Serial No. 529,526,

April 11, 1931. 1935, Serial No. 6,107

14 Claims.

The present invention relates to a method of and means for indicating direction, and more particularly to radio apparatus for indicating direction of an incoming signal wave, and is a continuation of co-pending joint application Serial No. 529,526, filed April 11, 1931.

Heretoiore it has been the practice in radio direction finding systems to employ unmodulated continuous wave transmission, interrupted continuous wave transmission, or spark transmission as a source of signal energy for which purpose special transmitting stations had to be provided, transmitting on certain fixed frequencies. Also, it was necessary to employ special receiving systems for the reception of the special signals.

One of the objects of the present invention is the provision of a novel method and apparatus whereby any source of radio signals, constituted either by modulated or unmodulated continuous waves, such as the ordinary transmitting stations broadcasting entertainment programs, as well as directional transmitting stations, such as beacon stations, may be utilized as a source of signal energy from which the position or heading of a mobile object carrying the apparatus may be determined with an equally high degree of precision.

Another object of the invention is to provide a novel radio receiving system which may be employed as an ordinary broadcast receiver for the reception of entertainment programs and/or weather reports, as well as a position finder and/ or radio compass.

Another object is to provide a novel method of employing modulated continuous waves, as for example, waves from radio broadcast stations, for obtaining visual indications of a selected intensity of signal without producing fluctuations in the indications due to modulation, from which indications the bearing of a mobile object may be determined.

A further object is to provide, in combination with a radio receiver adapted. for broadcast signal reception, novel means whereby the receiver may be employed for directional signal reception.

Another object is to provide, in combination with a radio receiving system adapted for broadcast signal reception of either modulated or unmodulated waves in a pluralityof frequency bands, 50 novel means whereby the system may be employed for directional reception in any one of said frequency bands.

Still another object of the invention is to provide, in combination with a standard broadcast receiver, a novel loop tuning system for direction- This application February 11,

a! reception for determining the position or bearing of a mobile object carrying the receiver, and means for so coupling the system to the receiver that distortion of bearing or direction due to insufiicient selectivity and/or a difference in phase 5 between the loop electromotive force and undesirable electromotive forces picked up by the loop system because of antenna effect is prevented.

Another object is the provision, in combination with a receiver of the above type, of novel means 10 whereby the receiver may be employed for directional reception of modulated continuous waves to produce either visual indications of a selected signal strength without fluctuations due to the modulation effect, or to produce audible reception 15 if desired.

Another object is to provide, in combination with broadcast receiver and a loop tuning system for employing the receiver for directional reception, a novel circuit arrangement whereby a volt- 2 age of heterodyning frequency and of relatively high amplitude as compared with the received signal frequency is introduced into the receiver or the loop tuning system to eliminate the modulation effect of the incoming carrier frequency, 25 that is, to eliminate the side bands of the incoming modulated continuous wave.

Another object is to provide, in combination with a receiver of the above type, novel visual indicating means having a high overload capacity whereby said means may be employed with the output circuit of the receiver in place of a sound reproducer, with the highest efiiciency.

Another object is to provide, in combination with areceiver of the above type embodying automatic volume control, that is, automatic control of the power output of the receiver, novel visual indicating means of variable sensitivity whereby the visual indications are maintained within a selected and/or limited range irrespective of the values of input signal voltages, which may vary over a wide range, as for example, when signals from low-powered or distant transmitting stations are received and when signals from nearby or high-powered stations are received.

Another object is to provide, in, combination with a receiver of the above type, a novel loop tuning system and switching means whereby the frequency range of the system may be varied without varying the number of turns of the loop, thereby affording the same amount of pick-up in the loop for each frequency range and maintaining the resistance of the loop at a minimum.

Another object is to provide, in combination with a broadcast receiver and a loop tuning systern for providing directional reception, novel means for obtaining electrical symmetry in the loop system and the input circuit of the receiver with respect to ground, whereby the antenna. effect of the loop system is eliminated.

A still further object is to provide, in combination with a broadcast receiver and a loop tuning system of the above type, novel means for rendering the loop non-directional for the purpose of ordinary radio reception.

Still another object of the invention is to provide in a radio direction finding system embodying a loop tuning system, a receiving system adapted to be employed either for directional'or' non-directional reception of modulated as well as unmodulated waves, an oscillation generator for introducing a heterodyning voltage into the receiving system for eliminating the modulation effect when reception of modulated continuous waves is employed, a novel method of loading the loop tuning system, the receiving system, and the oscillation generator so that equal changes in frequency in each of the systems will be obtained for equal increments of positional change in the tuning elements in said systemswhereby simultaneous tuning may be accomplished.

'Ihe above and other objects and advantages of the invention will appear more fully hereinafter from a consideration of the detailed description which follows, taken together with the accompanying drawings, wherein are illustrated two the present invention;

Fig. 2 is a circuit wiring diagram embodying the various features of the invention;

Fig. 3 is a circuit diagram of another embodiment of the invention, wherein the loop may be rendered non-directional 'for the purpose of ordinary reception;

Fig. 4 is a more or less diagrammatic view of one form of novel visual indicator which maybe employed in accordance with the invention; and

Fig. 5 is a curve showing the operational characteristicsof the indicator illustrated'in Fig. 4.

Referring now to the drawings, and more particularly to Fig. 1, the apparatus of the invention consists primarily of a rotatable loop antenna 4 mounted in any suitable manner and in any con-- venient location on the mobile object Whose position or direction is to be determined. A compass direction indicating device comprising a ring 5 marked with the cardinal comp-ass points and intermediate degrees is provided for indicating the position in azimuth of the l'oop' l when the selected signal intensity, as for example, a minimum and/or maximum signal is obtained by rotating the loop by means of the wheel 6. Slip rings 7 and 8 are provided for obtaining the electromotive force from the loop and introducing it into the loop tuning system 9. When a split loop is employed, as shown in Fig. 2, it will be apparent that four slip rings must be employed. Theloop' tuning system is coupled to a radio receiver Ill of any suitable type, which is adapted to rep-roduce broadcast programs from any of the transmitting stations now generally in operation and broadcasting entertainment programs. A sound reproducer or loud speaker I l of any suitable type is connected to the output of the receiver and a switch I2 is provided for switching the output circuit of the receiver from the loud speaker H to a visual indicator Ila. An oscillator I3 of any suitable type is connected to the system so that a heterodyne voltage of suitable frequency may be introduced into the receiver, fora purpose to be described hereinafter, when visual indications are to be employed instead of the sound reproducer for obtaining the selected signal strength. A switch l.4 is provided for disconnecting the oscillator from' the system when it is desired to employ the receiver for ordinary reception of entertainment programs or other broadcast reception through the loud speaker I I.

Referring now to Fig. 2, the receiver l0 may be of the usual type, preferably one in which automatic volume control is provided, and consists of two stages of radio frequency amplification RF -l and RF -2, a detector stage DET, and two stages of audio frequency amplification AF-l and AF-,-2. Vacuum tubes l5, [Sand ll employed asradio frequency amplifiers, and the detector, respectively, are shown as of the screen-grid indirectly-heated type generally known as the UY-224 type, while the first audio frequency amplifier i8 may be of the UY-227 type having a grid plate and indirectly-heated cathode or filament. The automatic control of the volume, or power output, oi the receiver may be accomplished by providing an automatic voltage bias on the grid of the vacuum tube IS in the second radio frequency stage derived from the output of the vacuum tube l8 of the first audio frequency stage. As illustrated, this maybe done by providing a connection from the plate of the vacuum tube It! tothe grid of the vacuum tube IS, in whichconnection are included resistance elements, as for example, R1, R2, and R of such value asto give the proper potential drop necessary to obtain the desired bias on the grid of the'tube I6. Inasmuch as the volume control arrangement per se is vnot the subject of the present invention and may be of any other type known in the radio art, it will be sufficient to state that the power output level of the tube I8v will be limited to a substantially constant predetermined maximum by virtue of the fact that in the event of an increased signal voltage being introduced in the input circuit of thevacuurn tube I6 the power output of the vacuumtube I8 will be increased, but as such powerincrease takes place in the vacuum tube l8 it will' cause an increased negative bias to be impressed on the grid of the vacuum tube [6, thereby making the grid more negative and reducing the amplification in said tube and accordingly decreasing the power output of the vacuum tube I 8. It isobvious, however, that any suitable type of receiver embodying any type of receiving vacuum tubes may be employed without departing from the scope of the inven i n.

In the embodiment illustrated, the two radio frequency stages and the detector stage of the receiver system are arranged to be tuned by means of the variometers 20, 2|, and 22, although a receiver employing variable condensers in the place of the variometers for tuning the circuits may be employed, if desired. Adjustable condensers 23, .24, and 25 are provided for aligning the three circuits into resonance throughout. the frequency range as determined by the capacity of the condensers andthe inductance of the variometers. Once the adjustment of the condensers 23, 24, and 25 is made, it remains fixed, and tuning is accomplished by means of the variometers, as hereinbefore stated. The loop antenna 4, which is provided for intercepting the signals and introducing the received signal voltage into the receiver, is preferably as large as the frequency range and the physical limitations of the mobile object on which the apparatus is mounted will permit. The loop is also designed to be of maximum inductance and minimum resistance and distributive capacity through the use of substantially heavy copper wire and careful insulation. The loop is arranged to be tuned by means of a variable condenser 25 connected in parallel therewith.

It is desirable, however, that the receiver be also capable of receiving signals transmitted from beacon stations or other stations which are in a frequency band below that of the transmitting stations broadcasting entertainment programs, and for this purpose a novel method of properly loading the circuits of the loop and the receiver is provided. The tuning elements of the various circuits, that is, the variometers 2!], 2|, and 22 and the variable condensers 29, are suitably interconnected mechanically to provide for simultaneous tuning. It will be noted, however, that the loop is tuned by means of a variable capacity, while the input circuits of the radio frequency stages and the detector stage are tuned by means of a variable inductance. It is for this reason that a novel method of loading the circuits is provided in order to obtain frequency alignment of the circuits; that is, that the frequency gradient or the frequency change per degree of each separate variable tuning .element be the same in the new frequency band determined by the loading, and that they all have some common datum from which they start at the same frequency. The method of loading, which may be termed inverse loading, consists in loading the inductively tuned circuits with capacity and loading the capacitatively tuned circuit, that is, the loop circuit with inductance. By inverse loading is meant that where two tuned circuits are employed and arranged to be tuned simultaneously and in one of which the frequency is changed by means of a variable capacity and in the other of which the frequency is changed by means of a variable inductance, if the former be loaded inductively then the latter must be loaded capacitatively and conversely, if the one circuit be loaded capacitatively, then the other must be loaded inductively in order to provide frequency alignment of the two circuits for simultaneous tuning in the new frequency band as determined by the loading. In this manner the products of inductance and capacity for each frequency in one circuit are always maintained equal to the products of the inductance and capacity in the other circuit for each increment of change in the variable tuning elements. In accordance with this method, loading condensers 26, 2i, and 28 are provided and are arranged to be connected in parallel with the condensers 23, 2d, and 25 by means of switches S1, S2, and S3, respectively, in order to properly load the variometer circuits. The loop circuit, on the other hand, is loaded inductively in order to cover efficiently all the frequencies in either of the broadcast band or the beacon band, and to this end the loop is preferably enclosed in a metallic (copper) housing (not shown) and wound in two separate coils, which may be connected in series for the beacon frequencies and in parallel for the broadcast frequency by means of the switches S4 and S5. In this way the inductance of the loop is changed without decreasing the amount of pick-up. The switches S1, S2, and S3 are preferably arranged for simultaneous operation so that all three circuits of the receiver and the loop circuit are shifted together from one frequency band to another. The audio frequency stages of the receiver are preferably so coupled as to give a remarkably wide frequency range.

In directional receiving systems wherein a rotatable loop is employed for obtaining a selected signal intensity, as for example, a maximum and/orminimum signal to determine the direction in azimuth of the incoming signal wave, the loop antenna is invariably located above the receiver and above the ground, which results in a signal being produced in the receiver regardless of the position of the rotatable loop, and thereby seriously masks the position of the loop, particularly when a minimum signal intensity is employed. This effeet is generally known as antenna effect and is almost invariably present in any type of directional antenna. Its effect is not only to mask the position of the loop for minimum and/or maximum signal, but to introduce false positions of minimum and/or maximum signal intensity due to the phase difference referred to above. For this reason it is desirable to provide absolute electrical symmetry between the loop with its tuning condenser and the ground by providing such identity of circuits from the loop to ground that the effects of currents from both sides of the loop circuit to ground effectively neutralize each other but in no serious magnitude alter the effects of the currents circulating in the loop and its tuning condenser, on the presence of which the directional properties of the loop depend. To obtain such absolute electrical symmetry of the loop and its tuning condenser with respect to ground, thus preventing distortion of obtained bearings due to difference in phase of the loop electromotive force and other undesirable electromotive forces picked up by the system, the loop circuit is provided with. small balancing condensers and 3|, which may be adjustable to provide correction for asymmetry in the loop windings, lead-ins, tuning condensers, etc., with respect to ground. For reasons of symmetry, coupling condensers 33 and 34, thepurpose of which will appear hereinafter, are fixed at equal values and are so constructed that their capacities with respect to ground are also equal, that is, their respective through impedances are equal as are their respective impedances to ground. For the further maintenance of symmetry with respect to ground, the filament circuit of the vacuum tube is connected to the electrical center of the variometer, while the grid of the tube is connected to one end of the Variometer. The electrical center may be defined as the point at which the potential with respect to one side of the input circuit is equal and opposite to the potential with respect to the other side of the input circuit, and at which point the resulting voltage will be zero when the point is connected to ground. A small variable condenser 32 is connected to the other end of the variometer and to its electrical center to balance the effect of the capacity between the grid and filament of the tube.

Means are also provided to secure high selectivity and sensitivity in the loop and associated tuning system throughout the several frequency ranges of the system. This is preferably accomplished by providing a loose coupling of the voltage capacity type between the loop circuit and the input circuit. In the embodiment illustrated, the coupling condensers 33 and 34 are employed for this purpose. It has been found that without such loose coupling, not only is the system relatively unselective and insensitive, but a large distortion of the incoming signal results, thereby producing two minima and/or maxima of signals which are in error with the exact direction from which the incoming signal is radiated and probably due to the two coupling humps (in the resonance curve) which invariably accompany excess coupling. By providing the condensers 33 and 34 and making them of appropriately small values, this undesirable result is prevented and a much higher selectivity and a sharper minimum are obtained with substantially constant values of these operational characteristics throughout the several frequency ranges.

An antenna 35 is provided, which may be employed for ordinary radio broadcast reception when it is not desired to employ directional reception, and 'may be connected to the system by means of the switch S6 which then renders the directional character of the loop 4 ineffective.

Another embodiment for non-directional reception is illustrated in Fig. 3, which will be described more fully hereinafter.

When it is desired to employ the visual indicator Ha for indicating the selected signal strength obtained by rotating the loop 4, as when directional reception of modulated waves is being accomplished, means are provided for preventing fluctuations of the needle of the indicator due to modulation; that is, for maintaining the response of the indicator substantially independent of the modulation, amplitude, and frequency which is being borne by the carrier frequency voltage applied to the loop. To this end a voltage of heterodyning frequency is introduced into the loop circuit as illustrated in Fig. 2, although the voltage may be introduced either into the amplifier or detector circuit of the receiver without affecting the method of operation. The oscillator I3 hereinbefore mentioned provides the necessary heterodyne voltage supply, and may be, in circuit arrangement, of the so-called Hartley type. It is provided with coupling means for supplying a substantially constant voltage to the receiving system independent of frequency. A variometer 36 is employed for varying the heterodyning frequency of the oscillator so that the latter may be properly aligned with the inductively tuned circuits of the receiver for simultaneous. tuning, and a loading condenser 31 is provided for changing the frequency band of the oscillator by connecting the condenser in parallel with the condenser 38 by means of the switch S7 so that the available heterodyning voltage may always be maintained within a few hundred cycles of the signal or carrier frequency; that is, when the receiver is shifted from the broadcast frequency band to the beacon frequency band. The oscillator may also be of the type wherein a variable capacity instead of a. variable inductance is employed for tuning, but in an oscillator of this type the condenser plates would have to be especially shaped in order to properly align the oscillator with the tuned circuits of the receiver which are tuned by variometers. This latter type of oscillator is shown at I3a, which may beemployed in the place of the oscillator 13 by operation of the switches S8, S9, and S10. The frequency band of the oscillator [31]. may be shifted by means of the switches S11 and S12 which introduce loading inductances into the circuit instead of loading condensers as in the oscillator l3.

By the introduction. into the loop tuning system from the oscillator of a voltage of heterodyning frequency of a relatively high amplitude as compared with the signal and the beating of this frequency and the carrier frequency in the detector stage, there are, of course, beats produced between the side bands and the heterodyne frequency, but because of the relatively lower amplitude of these beat frequencies as compared with the carrier beat frequency their effect is largely lost to the visual indicator and the indication in the latter is almost completely proportional tothe carrier frequency amplitude and substantially independent of the magnitude of the side band amplitudes. This diminution of the influence of the side bands is due not only to the rectification that takes place in the detector, but also to partial rectification taking place in the radio frequency stages due to the relatively great amplitude of the heterodyne frequency.

The primary requirements of this relatively simple method of modulation elimination consist, then, in the introduction into the system of a heterodyne frequency of relatively high amplitude and of the further amplification of the beating frequency output of the detector to such a level as will serve to actuate the output visual indicator.

In the operation of a radio direction finding system, it is desirable to provide for the reception of a Wide range of signal levels, this for the reason that signals which are received by the loo-p vary in strength, since relatively weak. voltages are obtained from distant stations and signals of relatively high voltages are obtained from nearby or high-powered stations. To this end it is, therefore, desirable to employ a receiver in which the power output is maintained more or less below a predetermined level and which may be accomplished in the manner hereinbefore described.

In employing a visual indicator or meter, it is desirable that the meter have a high overload capacity, so that it may be overloaded without being damaged in the event that the predetermined level which is maintained by the automatic control in. the receiver is higher than the capacity of the meter. This may be accomplished by providing a type of instrument having all the essential characteristics of the DArsonval galvanometer but modified as shown in Fig. 4 so that the pole pieces give a rapidly decreasing differential sensitivity as the moving coil approaches the end of its possible deflection on the high torque end. The instrument illustrated in Fig. 4 comprises the usual permanent magnet 42 having pole pieces 23 and M, between which a movable coil 45 wound on an iron core 46 is arranged to rotate in the usual manner. A pointer 4'! is supported by and movable with the coil 45 of a suitable marked scale it. Core 46, however, is so shaped as to have an elliptical section instead of the usual circular section commonly employed. Due to the particular shape of the core, the coil moves into a weaker magnetic field for a large deflection. In this manner, the indicator is made very sensitive for small deflections and relatively insensitive for large deflections, as indicated by the characteristiccurve shown in Fig. 5. The same effect may be produced by shaping the pole pieces instead of the armature core, or by providing eccentric motion of the coil or by high damping, or additional loading springs which control the movement of the coil.

Meter Ila, in the embodiment illustrated in Fig. 2, is of the direct-current type, and for this purpose a rectifier 39 is provided for changing the audio frequency currents from the output of the vacuum tube !9 into substantially uni-directional current, although it is obvious that an alternating-current meter may be employed.

Since the receiver is normally designed to work into a loud speaker, the impedance of which is approximately 5,000 ohms, means are provided for balancing the output impedance of the vacuum tube l9 and the impedance of the indicator circuit. In the form shown, said means comprise a transformer 40 and also include the rectifier 39, both sides of the transformer having their impedances approximately matched with their corresponding circuits; that is, the impedance of the primary matches the output impedance of the vacuum tube l9, while the impedance of the secondary matches the impedance of the rectifier and the visual indicator.

Referring to Fig. 3, there is illustrated an embodiment of the invention wherein switching means are provided for rendering the loop 4 nondirectional for purposes of ordinary reception of programs in the broadcast frequency band and is adapted to be employed where no non-directional antenna is available. In the form shown, said means comprise switches S13, S14, and S15, which are adapted to be actuated simultaneously. In the upward position switches S13 and S14 are arranged to short-circuit the loop 4 and tuning condenser 29 and switch S15 is arranged to insert tuning condenser 4| in series with the shortcircuited loop and the grid circuit of the first radio frequency stage. When switches S13, S14, and S15 are in downward position the tuning condenser 4| is disconnected from the circuit, and the loop 4 and the loop tuning condenser 29 are then effective to tune the circuit and impress the received signal voltage on the grid of the vacuum tube 5 of the first radio frequency stage;

Referring back to Fig. 2 for the operation of the system, the switches S1, S2, S3, S4, S5, and St are preferably so interconnected mechanical- 1y that they may be operated simultaneously to shift the receiver, the loop, and the oscillator from one frequency band to another frequency band in one operation; that is, by throwing a single switch lever in one direction, the series of switches will be thrown to adjust the system for reception of signals in the broadcast frequency band, while with the throwing of the single switch lever in the opposite direction, the switches will be thrown to adjust the system for reception of signals in the beacon frequency band. Switches Se and I 2, on the other hand, are arranged for simultaneous operation so that when the antenna is switched into circuit for non-directional reception the loud speaker II will be simultaneously connected to the output of the receiver, and the visual indicator Ila discon nected therefrom.

When it is desired to operate the system for receiving radio broadcast programs, the loop a tenna is first rendered non-directional by eithe closing the switch S6 to connect the non-direc tional antenna 35 to the receiver, or by throwing the switches S13, S14, and S1; in the embodi-- ment illustrated in Fig. 3, in the upward position,

thereby rendering the loop 4 non-directional in its receiving characteristics. The oscillator 13 is also cut out by opening the switches S8, S9, and S10. As pointed out hereinbefore, switches S6, S8, S9, and S10 are arranged for simultaneous operation by being connected to a common switch lever, so that the oscillator is disconnected at the same time that the loop 4 is rendered nondirectional. The switches S1, S2, and S3 are then opened so that the two radio frequency stages and the detector stages are adapted to receive signals in the broadcast frequency band. Any desired frequency may be tuned in by tuning the variometers 20, 2|, and 22, which are aligned for simultaneous tuning, as is the general practice in modern radio receivers. Switch I2 is also opened so that the transformer is disconnected from the output of the receiver and the Visual indicator rendered inoperative. The sound reproducer or loud speaker II is then effective to reproduce the incoming modulated continuous waves received by the antenna 35 or by the loop when the latter is rendered non-directional as indicated in' Fig. 3.

When it is desired to employ the receiver for directional reception on the broadcast frequency band, switches S1, S2, and S3 are left in the open position, and switch S6 is opened, thereby connecting the loop 4 to the input of the receiver. The loop tuning condenser 29 being also ganged to the variometers 20, 2|, and 22 and to the variometer 36 of the oscillator l3, the loop tuning system and the receiver may then be tuned to any known broadcasting station, and by rotating the loop 4, the intensity of the received signal may be varied until a selected signal strength, as for example, a minimum and/or maximum signal is obtained, as indicated in the sound reproducer or loud speaker H. However, in order to get a more perfectly defined minimum and/or maximum, the visual indicator Ha may be employed by closing the switch l2, which short-circuits the sound reproducer II. The oscillator I3 is then connected to the system by means of the switches S8, S9, and S10, which introduces the proper heterodyning frequency for eliminating the modulation effect of the incoming carrier wave so that fluctuation of the needie of the indicator Ila is prevented.

F'or determining the location of the mobile object on which the receiver is mounted, it is first necessary that there be at least two radio trans mitters of known position operating within satis factory receiving range of the equipment. It is found desirable to search out these available transmitters by means of the non-directional audible type of reception and thereby determine the source of signals that are available, and from such data as may be at hand, to locate the positions of the stations themselves on maps provided as a part of the position finding equipment. When at least two stations have been found operating satisfactorily and fairly continuously, the loop tuning system is adjusted until the output indicator Ha shows the presence of e slgnal- The oscillator is also simultaneously adjusted so that heterodyning frequency is. of such a value as to give the increase in signal output that accompanies heterodyning reception. Further and careful adjustment of the receiver, controls may then be made again in order that the highest sensitivity to the signal and signal change is obtained. It will sometimes be found that the nal intensity is too great for satisfactory opof the visual indicator, and. at this point M it is then necessary to adjust the manually operated Volume control of the receiver until less than full scale reading is secured on the output meter. Then, in order to Orient the source of the signals relative to the mobile object, the loop 4 is rotated until an indication of the selected signal strength is obtained on the indicator. Where no automatic control of volume is provided within the receiver, further manipulation of the manual volume control during the rotation of the loop will usually have to be resorted to so that the sensitivity of the receiver is kept at such a value as will give the maximum sensitivity to small changes in input voltages as the loop is swung into the position in which it is exactly broadside to the signal wave front and the signal voltage induced in the loop appoaches zero. When once the zero position has been found, the radio compass reading 'on the ring 5, as well as the ships bearing as given on the ships compass, are noted. The operation is then repeated in making observations of the orientation of the second source of radio signals, and similar compass readings taken. With these data available, the location of the mobile object is determined on a chart by the intersection of the two lines of direction as determined by the compass readings and the location of the transmitting stations on the chart. For greater precision, three observations may be made and the triangle of errors thereby determined, and a more precise location of the mobile object fixed upon.

It if be desired to employ a beacon transmitted as a source of signal -energy from which to determine the bearing of the mobile object, the switches S1, S2, and S3 are closed so that the radio frequency amplifier circuits and the detector circuit are 'capacit'atively loaded and the frequency band of the receiver shifted to a lower range of frequencies. The loop '4 is then rotated to obtain minimum signal intensity, in the same manner as before. Once knowing the position of the mobile object on the chart, a known beacon transmitter may be selected and a minimum signal intensity obtained. The mobile obj ect may then be steered toward the beacon transmitter by keeping the mobile object on a course such that the visual indicator'gives a continuous minimum signal intensity indication. In this mannor, the receiving system with the visual indicator may be employed as a compass, and "a mobile object steered towards a known destination; that is, the beacon station. The system may also be used in this manner by employing a "broadcast station 'as the known destination.

From the foregoing it will be apparent that there is thus provided a novel method and apparatus whereby any source 'of modulated contiiiuou's 'waves, such as the ordinary broadcast stations, may be utilized 'as a source of signal energy from which the Ep0siti0nor heading i of a mobile object "carrying *the apparatus *may be determined.

The novel method consists primarily in -cbtaining a visual indication of a selected signal intensity, preferably a minimum, irom lmodulated continuous waves by receiving the modulatedwaves, impressing avoltage ofheterodyne frequency-on the"modulated vwaves wherebythe modulation of the incoming carrier -,wave ,is eliminated, translating the "resultant wave 51 an "audible frequency wave, and producing a visual V indication from I the audible frequency wave.

There is also provided a novel radio receiving system which may be employed as an ordinary broadcast receiver for receiving entertainment programs as well as a position finder and/or radio compass, and embodying a novel arrangement and cooperation of circuits and elements whereby several electrical circuits are controlled with the least number of controls at maximum efliciency to obtain the desired result.

While only two embodiments of the invention have been illustrated, other changes and modifications in circuit arrangements, which will now appear to those skilled in the art, may be empl'oy'ed without departing from the scope of the invention. The loading of the loop antenna systern, for example, may be accomplished by inserting inductanc'es into the circuit, and the variometcrs 29, 2|, and 22 may be replaced by variable condensers ganged iorsimultaneous tuning, and circuit loading of the two radio frequency stages and the detector stage may then be accomplished also by inductive loading instead of capacity loading as illustrated in Fig. 2. Reierence will, therefore, be had to the appended claims for a definition of the limits of the invention.

What is claimed is: I 1. In a radio direction finding system th method of obtaining a non-fluctuating visual "indi'cation of a selected intensity of signal from modulated continuous waves, which consists in receiving the modulated continuous waves, impressing a voltage of het'e-rodyning frequency on the modulated continuous waves, said voltage having an amplitudeand frequency such that the modulation eiiects of the incoming carrier wave are eliminated, translating the resultant wave into an audible frequency wave, and producing a visual indication from said audible frequency wave.

2. In a direction finding system the method of obtaining a steady visual indication of a selected intensity of signal from modulated continuous waves, which consists in receiving the modulated continuous waves, impressing a voltage of heterodyning i-re'mien'cy on the modulated continuous waves, said voltage being of relatively high amplitude as compared with the received signal frequency whereby the modulation effects of the incoming carrier wave are eliminated, translating the resultant wave into an audible irequency wave, and producing a visual indication from said audible (frequency wave.

3. In a direction finding system the method of obtaininga visual indication of a selected intensity of signal from modulated continuous waves, which consists in receiving the modulated continuous wavesimpressing a voltage 'ofheterodyning frequency on the modulated continuous waves, said voltage having an amplitude and frequency such that the modulation eiiects of the incoming-carrier wave are eliminated, translating the resultant wave into an audible irequency wave, rectifying the audible frequency wave to produce substantially uni-directional current, and employing said unidirectional current to produce a visual indication of the selected intensity of signal.

l. In a direction finding system the method of obtaining a visual indication of a selected intensity of signal from modulated continuous waves, which consists in receiving the modulated continuous waves, impressing a voltage of high frequency on the modulated continuous waves, said voltage being of relatively high amplitude as compared with the received signal-frequency whereby the modulation effects of the incoming carrier wave are eliminated, translating the resultant wave into an audible frequency wave, rectifying said audible frequency wave to produce substantially uni-directional current, and employing said uni-directional current to produce a visual indication of the selected intensity of signal.

5. The combinatitn a direction finding system of a receiving system adapted to receive modulated continuous waves, a directional antenna system operatively connected with said receiving system for obtaining a selected intensity of signal, a visual indicator, means for connecting said visual indicator to said receiving system to indicate when the desired signal intensity is obtained, means for afiecting said receiving system so that the modulation effects of the incoming continuous wave are eliminated, thereby preventing fluctuations in the indicator, and means for indicating the direction of the incoming waves when the selected signal intensity is obtained as indicated by the visual indicator.

6. The combination in a radio direction finding system, of a receiving system adapted to receive modulated continuous waves, a loop tuning system operatively connected with said receiving system for providing directional reception of said waves, visual means for indicating the intensity of the received signal, means for eliminating the modulation effect of the incoming modulated waves whereby fluctuations in the indicating means are prevented, and means for obtaining electrical symmetry of the loop system and the input circuit of the receiver with respect to ground.

'7. The combination in a direction finding system, of a receiving system adapted to receive modulated continuous waves, a loop tuning system for providing directional reception, visual means for indicating the intensity of the received signal, means for eliminating the modulation efiect of the incoming modulated waves Whereby fluctuations in the indicating means are prevented, and means for-obtaining electrical symmetry of the loop system and the input circuit of the receiving system with respect to ground, said last mentioned means including a condenser connected to each of the input leads between the loop and the receiving system and to ground, and means for balancing the capacity between the grid and filament of the first vacuum tube of the receiver.

8. In a radio direction finding system, the method of obtaining a non-fluctuating visual indication of the direction of an incoming signal from modulated continuous waves, which consists in receiving the modulated continuous waves, impressing a voltage of heterodyning frequency on said waves, said voltage having an amplitude substantially equal to or greater than that of the received signal frequency, whereby the modulation eifects of the incoming carrier wave are eliminated, and producing a visual indication from the resultant wave.

9. In a directional radio receiving system for receiving modulated continuous waves, the combination of a visual indicator operatively associated with said receiving system for indicating the relative direction of the incoming waves and having a pointer adapted to fluctuate in accordance with the modulations of said waves, and means coupled with said receiving system for eliminating the modulation effects of said Waves whereby fluctuations of the pointer are prevented.

10. In a directional radio receiving system arranged to receive modulated continuous waves, the combination of a visual indicator operatively associated with said receiving system for indicating the relative direction of the incoming waves and having a pointer adapted to fluctuate in accordance with the modulations of said waves, and means associated with said receiving system for eliminating the modulation effects of said waves whereby fluctuations of the pointer are prevented, said means comprising an oscillator for impressing on said modulated waves a heterodyning voltage having an amplitude the value of which is substantially equal to or greater than that of the received signal frequency.

11. The combination with a directional radio receiving system for determining the direction of the source of a received modulated carrier wave, of means for impressing on said received carrier wave an alternating voltage having an amplitude the value of which is substantially equal to or greater than that of the incoming signal frequency, whereby the modulation effects of said carrier wave are eliminated.

12. The combination with a directional radio receiving system for determining the direction of the source of a received modulated carrier wave, of an oscillator for impressing on said received carrier wave an alternating voltage having an amplitude the value of which is substantially equal to or greater than that of the incoming signal frequency, whereby the modulation effects of said carrier wave are eliminated.

13. In a directional radio receiving system for receiving modulated carrier waves and including a loop antenna, the combination of a visual indicator connected in said receiving system for indicating the intensity of the received waves, which intensity varies with a change in position of the loop with respect to the direction from which said waves are received, and means for eliminating the modulation effect of said carrier waves whereby fluctuations in the indicator due to modulation of the carrier wave are prevented.

14. The combination with a radio receiving system for receiving modulated carrier waves, of a visual indicator connected in said receiving system for indicating the intensity of said received waves, and means for introducing into said receiving system and impressing on said received waves an alternating voltage having an amplitude and frequency such that the modulation effects of said carrier waves are substantially eliminated, whereby fluctuations in the indicator due to said modulation effects are prevented.

LAWRENCE C. F. I-IO-RLE. 

